The present invention relates generally to the field of ink jet printing, and more particularly to an ink jet printer having means for priming the nozzles of the printer in the event that they become depraved and fail to operate on demand.
The technology of ink jet printing has become well known and printers of many sizes and configurations have become commonplace in various printing applications. This technology provides a relatively simple form of printing apparatus which yields rapid and substantially high quality print for the extent of printing apparatus complexity, and attendant cost, involved. These qualities render ink jet printing technology and apparatus based hereon highly suitable for a variety of printing applications, particularly computer deck top publishing, graphic plotters and textile printing,
In order to better understand the problems which are solved by the present invention, it is necessary to have a basic familiarity with the principles of ink jet printing, and how the printer head works. Although there are several types of ink jet printers in general use, for the purpose of illustration the principles of ink jet printing will be explained in connection with the type of ink jet printer in which the present invention is intended for use, it being understood, however, that the present invention is applicable to any of the other types of ink jet printers. Generally speaking, ink jet printing involves he use of a print head having a matrix of very small nozzles arranged on a nozzle plate in very closely spaced relationship and spanning the distance over which a line of print, or other graphic representation, is to appear on paper. The print head includes a reservoir of ink which communicates through individual conduits with a plurality of very small chambers, one for each nozzle, through which the ink flows to reach the nozzles. Each chamber contains a small, high energy resistance heating element which is responsive to a minute electrical current to heat almost instantly to a sufficiently high temperature to volatilize the solvent in the ink and thereby create a small bubble in the ink adjacent the heating element. The momentary increase in pressure in the ink within the chamber resulting from creation of the bubble is sufficient to force a small amount of ink from the nozzle connected to the chamber and a tiny droplet of ink is deposited on the paper adjacent to the nozzle. The actual printing of any form of text or graphic material on a piece of paper is the result of extremely rapid control over the plurality of heating elements in a predetermined sequence under the control of suitable software and relative movement between the paper and the print head, to deposit droplets of ink in a pattern which will yield the desired image.
A significant problem that arises with this type of printing apparatus is that the nozzles may become deprimed from time to time, which means that a minute quantity of air gets into the nozzles adjacent the nozzle plate and prevents ink from being ejected therefrom in response to energization of the heaters during a printing operation. There are several factors which contribute to the possibility of the nozzles become deprimed, including ink solvent volatilizing in the nozzles adjacent the nozzle plate from lack of use of the printing apparatus for an extended period of time, some form of shock to the printing apparatus which breaks the air/ink interface and allows aid to enter the nozzles, printing a highly dense image, such as a picture or graphic, which tends to expel ink from the nozzles at a rate faster than that at which it can be replaced from the reservoir, resulting in a slight back pressure at the nozzle, thereby causing air to enter the chamber, and printing in a high ambient temperature environment which lowers the viscosity of the ink and thereby results in ink being expelled from the nozzles at the rate faster than that at which it can be replaced.
For whatever the reason, if the nozzles become deprimed, the print head will not operate properly, if at all, due to the lack of ink at the nozzles at the beginning of a printing operation. It is essential for proper operation of the print head that the air/ink interface remain precisely at the surface of the nozzles on the nozzle plate; if the air/ink interface breaks down for any reason and a minute amount of air becomes entrapped in the nozzles or in the ink conduits adjacent to the nozzles, the minute hydrostatic pressure built up in the heating chambers by the momentary energization of the heaters, and the correspondingly small bubble generated therein, is ineffective to force sufficient ink through the conduits and nozzles to reestablish a flow of ink to achieve printing. It then becomes necessary to reprime the nozzles, which is typically accomplished by effectively attaching a vacuum system to the print head to pull ink from the reservoir through the conduit/chamber system and out through the nozzles, thereby reestablishing the air/ink interface at the nozzle plate.
This problem has been addressed numerous times in the past and many different attempts to find a satisfactory solution can be found in the art. For the most part these solutions have involved a vacuum system built into the printing device which involved a relatively complex arrangement of a pump, a motor, tubing to communicate between the pump, the print head and a waste reservoir for excess ink pulled through the system. These arrangements generally were expensive, added an undesirable degree of complexity to the printing apparatus in which they were installed, thereby creating maintenance and packaging problems and wasted a considerable amount of ink over an extended period of time. Thus there is a need for a simple, inexpensive add easy to operate manual ink priming device which can be installed in existing ink jet printing devices with little or modification thereto, and which require little or no maintenance.